Trueness of intraoral scanning of edentulous arches: A comparative clinical study

To compare the accuracy of intraoral scanning (IOS) of the edentulous arch with the hybrid protocol of cast digitization (CD), and to investigate the effect of arch type and area on trueness.

Participants that were edentulous in both arches were recruited. Two impression protocols were used; the IOS as the test protocol with an IOS device (TRIOS 4; 3Shape, Denmark), and the CD as the control, including tracing compound (TRACING STICKS; Kemdent, UK) for border molding, polyvinyl siloxane (Hydrorise Monophase; Zhermack, Italy) for impression, and cast digitization with a laboratory scanner (ceramill® map400, AMANNGIRRBACH, Germany). Scanned files were exported to a 3D inspection software (Geomagic Control X; 3D Systems, NC) for trueness analysis. The CD file (reference file) for each participant was split into 2 areas; the dynamic area representing the mobile tissues at the peripheral border, and the static area representing the rest of the arch. Statistical analyses were performed with 1-sample t-test for the difference between CD and IOS protocols, paired sample t-test for the difference between the static and dynamic areas for each arch, and an independent sample t-test for the difference between the maxillary and mandibular arches for each area, with α = 0.05. Effect size was calculated with Cohen's d (d), with 0.2 as small, 0.5 as medium, and 0.8 as large.

A total of 21 participants were included. The difference between the IOS and CD protocol was significant for all subset comparisons (p < 0.001, d: 2.5-6.2, large effect size). Dynamic areas had lower trueness in comparison with static areas (p < 0.001, d = 4.57, large effect size for the maxillary arch, p < 0.001, d = 3.96, large effect size for the mandibular arch). Mandibular arch had lower trueness in comparison with the maxillary arch (p < 0.001, d = 1.45, large effect size for the static areas, p = 0.009, d = 0.85, large effect size for the dynamic areas, p < 0.001, d = 1.71, large effect size for all areas). Color difference map showed marked positive deviation in the buccal dynamic areas of both arches, and nonmatching areas with evident overstretching.

While the IOS of edentulous arches could be feasible for attached mucosa, providing a functional shape for the peripheral border remains a challenge, with a thinner and more outward border for the IOS in comparison with the CD protocol. The IOS of the mandibular arch is more difficult and has lower trueness in comparison with the maxillary arch.